The present invention relates to a laser thermal control system, and more particularly to a variable emissivity laser thermal control system. Emissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature and under similar conditions.
A laser is a thermal device which is extremely sensitive to temperature variations. As the wall temperature of a laser increases from an optimal value, the output power capability of the laser (in watts) significantly decreases. Typically, metal vapor lasers operate optimally only in a range within .+-.30.degree. C. of a desired temperature. The insulation used in metal vapor lasers is typically within 20% of its nominal value. This is the tolerance of the insulation and not subject to modification. As a result, the pulsed power electronics which drives a metal vapor laser is typically designed to provide pulsed power above the maximum thermal operating point of the laser. This takes into account the insulation tolerance. Thus, prior art lasers are usually designed with a sub-optimal amount of-insulation. With too much insulation, or even optimal insulation, a prior art laser may operate at excessively high temperatures, requiring a reduction in input power to run the laser at the proper operating temperature. With too little insulation, a prior art laser operates at excessively cold temperatures, even with maximum power electronics input. The lack of sufficient insulation results in an inability to achieve a proper laser operating temperature even with maximum pulsed power input. Currently, lasers are operated at about 20% more insulation than is necessary in order to reduce the input pulsed electronics power and still achieve proper operating temperatures. Prior art laser power supplies are thus operated at less than their maximum capacity and consequently underutilize the available pulse power electronics.
The disadvantages of the temperature constraints on prior art lasers are overcome in accordance with the present thermal control system which enables a laser to operate at its full pulsed electronics power. In this regard, the thermal control system is designed to operate at a power level that corresponds to the aforesaid tolerance level of the insulation. In short, to maintain the same laser optimal operating temperature, the input power delivered to the prior art laser is reduced. In accordance with this invention, full pulsed electronics power, e.g. 40 KW, is input into the laser, then the laser operating temperature is gradually increased using a variable emissivity system of vanes and foils until the optimal temperature is attained. If higher power is input into the laser, such as 50 KW, the prior art result would be higher temperatures and eventually lead to a decline in laser output power; however, in this laser, the operating temperature is reduced using the variable emissivity system. Lasers designed in accordance with the present invention operate much more efficiently than the methods and apparatuses of the prior art. In the prior art, only about two-thirds of the available pulsed electronics power is utilized for driving the metal vapor laser. Because metal vapor lasers are expensive to build and operate, the aforementioned limitations are significant factors to consider for monitoring the cost and performance of lasers.